Causes of swelling under the tongue can be due to salivary gland disorders such as sialolithiasis, sialadenitis, viral infections, cysts and malignant tumors. Other causes include Sjogren's syndrome, benign tumors and sialadenosis, according to WebMD. Viral illnesses that cause swellings include the Epstein-Barr virus, cytomegalovirus, coxsackievirus and the human immunodeficiency virus.
Sialolithiasis occurs when calcium-rich stones form inside the salivary glands, and its causes include dehydration, low food intake leading to the production of less saliva or medication that decreases saliva production, as reported by Drugs.com. When the stones partially or completely block the gland duct, then there is pain and swelling. Sialadenitis is the infection of a salivary gland caused by bacteria. Common with elderly patients, it can also be present in infants.
Viral infections affect the whole body system but affect the salivary glands by causing swelling, pain and difficulty when eating, according to Healthline.
Most babies are born with cysts in their parotid glands, which can later develop into ear problems, WebMD reports. Other forms of cysts form on the salivary gland later in life, causing infection and salivary gland stones.
Another cause of swelling is Sjogrens syndrome, according to WebMD. It is an autoimmune disorder that attacks the salivary glands and the lacrimal glands. Swelling under the tongue can also be due to malignant tumors from salivary gland cancer.